Tumor necrosis factor alpha (“TNF-alpha”) is a cytokine produced by many cell types such as monocytes and macrophages. See e.g., Old, L. Science 230:630-632 (1985). TNF-alpha plays an important role in many biological processes and has been implicated in the pathophysiology of a variety of other human diseases and disorders, including sepsis, infections, autoimmune diseases, transplant rejection and graft-versus-host disease. See e.g., Vasilli, P., Annu. Rev. Immunol. 10:411-452 (1992); and Tracey, K. J. and Cerami, A. Annu. Rev. Med. 45:491-503 (1994).
In an effort to treat/prevent these diseases, various therapeutic strategies have been designed to inhibit or counteract TNF-alpha activities. U.S. Pat. No. 6,090,382 disclosed human antibodies (e.g., recombinant human antibodies) that specifically bind to human TNF-alpha with high affinity and slow dissociation kinetics. Nucleic acids, vectors and host cells for expressing the recombinant human TNF-alpha antibodies were also disclosed. One example of such recombinant TNF-alpha antibodies is called Adalimumab, which is marketed under the trade name Humira®. The entire contents of U.S. Pat. No. 6,090,382 is hereby incorporated by reference into the present disclosure.
Recombinant biotherapeutics are typically produced by live cells and are inherently more complex as compared to traditional small molecule drug. Various post-translational modifications have been reported as major contributors to heterogeneity in recombinant monoclonal antibodies (References 1-4). Some of these modifications, for example, glycosylation and sialic acid incorporation, may occur during fermentation (References 5-7). Some other modifications, such as oxidation and disulfide bond scrambling, may occur during production, purification and storage.
One example of such modifications is the so-called acidic species (charge variants). Acidic species are observed when recombinant monoclonal antibodies are analyzed by weak-cation exchange chromatography (WCX) (FIG. 1). One major contributing factor is the removal of the C-terminal lysine of the heavy chain by cell-derived carboxypeptidease, reducing the overall positive charge (Reference 8). These variants are commonly referred to as Lys0, Lys1 and Lys2 species, respectively.
C-terminal amidation (Reference 9) is another enzymatic process during fermentation. Another type of variant is caused by spontaneous non-enzymatic transformations, which include the formation of pyruglutamate (Pyro-Glu) from an N-terminal glutamine (Gln) that remove the positive charge of the free N-terminus (Reference 10), and the deamidation of asparagine (Asn) to aspartic (Asp) or isoaspartic acid (isoAsp or isoD) that introduces negatively charged carboxylic acids (References 11 and 12).
Some modifications may shift the retention time of antibody on weak cation exchange chromatography even though they do not alter the formal charges of the antibody molecule. These modifications may exert their effects through perturbation of local charge and conformation. For instance, incomplete glycosylation (Reference 13) or the presence of free sulfhydryl (References 14-16) may shift the retention time of antibody on weak cation exchange chromatography. It is worth noting that some modifications are imparted by metabolites, such as glycation by glucose, methionine oxidation by reactive oxygen species (ROS), cysteinylation by cysteine (Reference 17), and S-homocysteinylation and N-homocysteinylation by homocysteine (References 2, 18-23). Although the mechanisms of many modifications have been reported, these mechanisms cannot fully explained the observed heterogeneity of recombinant monoclonal antibodies on weak cation exchange chromatography.